The Murder of Mr. Moore

Detective Derek was reviewing notes on the murder of Mr. Moore as he was heading to the police station to interrogate the suspects. The victim was Mr. Moore, a very powerful billionaire. He was shot square in the forehead around 11:00 PM the previous day. Mr. Moore had 3 sons, Bob, Jack, and John, who were possible suspects. These sons were strapped for money so each had a motive for killing Mr. Moore.
As Derek entered the police station, he was led to the interrogation room where he met two of the sons, Bob and Jack. He heard out their testimonies. "Jack and I decided to hang out with our old man," said Bob. "My dad, Jack, and I went to a restaurant about 15 minutes away. We came back around 11. As we entered the mansion, John, out of nowhere, started running toward the mansion. It startled Jack and me, but my dad hadn't noticed because he was a bit drunk. When I noticed John had a gun, I tried to warn my dad but John shot him before my dad could even turn around and look at him."
Detective Derek asked, "Jack, do you confirm his testimony?"
Jack replied, "Yes."
Detective Derek then said, "Because you have lied to me, you two are both prime suspects in the murder of Mr. Moore."
How did Derek know Jack and Bob were lying and were involved in the murder?

Hint

Answer

The notes Detective Derek read said that Mr. Moore was shot "square in the forehead". For that to be true, the shooter would've been standing in front of Mr. Moore, not behind him. Because Mr. Moore did not have time to look back at John, Detective Derek knew John could not have shot Mr. Moore in the forehead. Bob and Jack seemed more likely suspects because they were with Mr. Moore at the time of the murder. The two confessed to the murder because they needed the inheritance for their gambling habits. When they saw John walk by the mansion on his late night stroll, they decided to pin the murder on him.Hide